The maintenance, improvement, and amelioration of the brain function are desired by wide generations of people from the youth to the aged. The maintenance, improvement, and amelioration of the memory and the learning ability are important not only for students and working adults studying for entrance and qualifying examinations, but also for conducting daily work and life. The aged desire to prevent the decline of the brain function and maintain, improve, and ameliorate the brain function because the decline of the memory and/or the cognitive function affects quality of life.
Furthermore, the increase of the mental disorder caused by the decline of the brain function associated with the aging in the aged has become a social issue as a result of increase of the aged. Diseases caused by the decline of the brain function include not only dementia represented by Alzheimer's disease, but mental diseases such as depression and delirium have been also reported to be caused by the decline of the brain function (Non-Patent Literature 1 to 3).
The search for substances that increase the brain function has been increasingly conducted as the elucidation of the brain function progresses. in particular, analyses of food ingredients searching for substances that improve the brain function have been conducted since food ingredients are considered to cause no side effects.
For example, an epidemiological investigation of the age group of 39 to 65 years old conducted in Australia has given the result that daily intake of a fermented dairy product enhances the memory (Non Patent Literature 4). The result that the prevalence of cognitive impairment is decreased by intake of a fermented dairy product has been obtained also in the United States of America (Non Patent Literature 5). It is considered from these results that a substance that enhances the memory and learning function and the cognitive function is contained in fermented dairy products. However, these research results are those of epidemiological investigations and the actual active ingredient(s) and the mechanism of action remain unknown.
Identification of the ingredient that enhances the brain function, for example, maintain, improve, and/or ameliorate the memory and learning function and/or the cognitive function in foods that can be consumed daily, should be useful for people in wide generations. Since fermented dairy products are considered to contain an ingredient that enhances the memory and learning function and the cognitive function as described above, products available for wide range of people from the youth to the aged can be developed by identifying the ingredient and use it as a medicament or a food.
Microglia, which are the only immune cells in the brain, have found to have the functions that are essential for maintaining the homeostasis in the brain, such as the phagocytotic removal of waste materials in the brain and the restoration of injured tissue. While the waste material removal in the brain and the promotion of generation of synapses by microglia contribute to the maintenance, improvement and amelioration of the cognitive function, it has been reported that the excessive activation of microglia may induce an inflammatory state and cause the decline of the cognitive function (Non-Patent Literature 6 to 9). Inflammatory cytokines and chemokines, such as TNF-α or the like, produced by excessively activated microglia have been reported to be closely related to morbid states such as pain, depression, and chronic fatigue (Non-Patent Literature 10 to 16). Therefore to control microglial activity is important in preventing arid treating various diseases associated with the brain.